1. Field of the Invention
The present invention relates to a plating-free solid wire for MAG welding, not subjected to a plating treatment such as copper plating. More particularly, it relates to a plating-free solid wire for MAG welding, capable of extremely reducing the amount of spatters to be generated in semiautomatic welding or automatic welding.
2. Description of the Background
In general, the term xe2x80x9cMAG weldingxe2x80x9d denotes the welding using 100% CO2 as a shielding gas, or the welding using such a predominantly Ar-based mixed gas as to contain an oxidizing gas such as a CO2 or O2 gas in an amount of 10 to 30%. As the cause of a large difference in amount of generated spatters according to the shielding gas, mention may be made of a variation in transfer mode of droplets. For the CO2 welding, the principal transfer mode is globular transfer. In contrast, for the predominantly Ar-based mixed gas welding, the principal transfer mode is spray transfer. Therefore, the amount of generated spatters is largely reduced, and excellent characteristics can be obtained also in terms of arc stability. Further, by allowing a K compound which is an alkali metal to be present on the wire surface as an arc stabilizer, it is also possible to still further stabilize the arc. The following reason may be mentioned as to why the alkali metal contributes to the stabilization of arc. Namely, the gradient of arc potential lowers to facilitate creeping-up of the arc to above the droplets. As for such an effect due to the alkali metal, the technology typified by Japanese Patent No. 1881911, or the like has already been reported.
Whereas, for polyisobutene, JP-A No.157858/1996 discloses a technology in which fats and oils sulfurized by a sulfurizing agent prevent the abrasion of a feeding chip. On the other hand, JP-A No. 158669/1998 discloses a technology in which use of polyisobutene as a viscosity index improver prevents the abrasion of a feeding chip.
Therefore, in accordance with an extension of prior art, the presence of a proper amount of K compound or oil on the wire surface is considered optimum for a further quality improvement in MAG welding, regardless of the presence or absence of copper plating.
Prior-art solid wires for MAG welding are mostly copper-plated wires. The reason why copper is plated is to ensure electric conductivity, to improve the rust resistance, and the like. However, it has been revealed that a copper-plated steel wire provides a larger surface tension of a droplet because of the higher copper concentration of the droplet surface as compared with a wire whose steel base is completely exposed, i.e., a non-copper-plated wire. The present inventors have observed an arc phenomenon in MAG welding using a high-speed video camera capable of taking 2000 frames per second. As a result, it has been shown that the droplets of the copper-plated wire transfer in the following mode. Each droplet tends to increase in diameter along the vertical direction, so that a reduction in diameter of the droplet is not achieved. This is presumably due to the following fact. Namely, there occurs a phenomenon wherein the increase in diameter of each droplet causes an instantaneous short-circuit between droplets or between droplets and molten pool during spray arc, which facilitates the spatter generation. In contrast, droplets of the non-copper-plated wire transfer in the following mode. Namely, no copper is present on the droplet surface, and hence the surface tension of the droplet is reduced, resulting in a reduction in diameter of the droplet. Accordingly, an instantaneous short-circuit will not occur between droplets or between droplets and molten pool during spray arc, resulting in a reduced amount of generated spatters. The wire on the surface of which a K compound and MoS2 are allowed to be present for further reducing the amount of spatters to be generated under the condition of such a non-copper-plated wire surface, is disclosed in JP-A No. 104883/1999.
However, in actual welding wherein a wire should be fed in units of several hundred kilograms with stability, only by applying the K compound and MoS2 on the plating-free wire surface, the following problem has become obvious. Namely, the K compound and MoS2 drop off from the wire surface, and accumulate in a conduit liner. Accordingly, the wire feedability gradually becomes unstable.
Namely, no matter how hard the arc stabilization and a still lower spatter level due to the K compound and MoS2 are pursued, it is not possible to sufficiently obtain these effects under the conditions where the wire feedability during welding is unstable.
The present invention has been completed in view of such circumstances. It is therefore an object of the present invention to provide a plating-free solid wire for MAG welding, which is capable of reducing the amount of spatters to be generated while maintaining excellent lubricating properties and feedability even during large-volume feeding.
In one aspect, we provide a plating-free solid wire for arc welding that includes: pits each having an opening on the circumferential surface of the wire, and being wider inside than at the opening, and/or pits each having a portion not to be irradiated with an externally incoming light; and a sulfide and an oil containing polyisobutene present in the inside of each of the pits and/or on the wire surface, the oil containing polyisobutene being present in an amount of 0.1 to 2 g per 10 kg of wire.
Incidentally, in this specification, the xe2x80x9cpits each having an opening on the circumferential surface of the wire, and being wider inside than at the openingxe2x80x9d are referred to as xe2x80x9cbottleneck-like pitsxe2x80x9d. Whereas, the xe2x80x9cpits each having an opening on the circumferential surface of the wire, and having a partial inside not to be irradiated with an externally incoming lightxe2x80x9d are referred to as xe2x80x9ccave-like pitsxe2x80x9d.
FIG. 1 is a cross sectional view of a wire, showing the xe2x80x9cbottleneck-like and/or cave-like pitsxe2x80x9d. As shown in FIG. 1, the wire is characterized by having a portion which is shadowed and cannot be seen from the surface (the portion filled in with black in FIG. 1), when it is assumed that there is a virtual light source whereby light rays are projected onto the wire surface along the radial direction toward the center.
In another aspect, we provide the plating-free solid wire for arc welding wherein: the pits are preferably present one at each of not less than 20 spots in total per circumference length along a given wire circumference.
In another aspect, we provide the plating-free solid wire for MAG welding wherein: the effective length ratio of the pits is preferably not less than 0.5% and less than 50%.
In another aspect, we provide the plating-free solid wire for arc welding wherein: the oil containing polyisobutene is preferably present in an amount of 0.1 to 2 g per 10 kg of wire.
In another aspect, we provide the plating-free solid wire for MAG welding wherein: MoS2 having a particle diameter of 0.1 to 10 xcexcm is present as the sulfide in the xe2x80x9cbottleneck-like and/or cave-like pitsxe2x80x9d, i.e., on the wire surface or immediately under the wire surface, and the coating weight of the MoS2 is 0.01 to 0.5 g/10 kg.
In another aspect, we provide the plating-free solid wire for arc welding wherein: a K compound is present in the pits and/or on the wire surface, and is present herein in an amount in terms of K of 2 to 10 mass ppm based on the total mass of the wire.
In another aspect, we provide the plating-free solid wire for arc welding wherein: the K compound is preferably potassium borate.
In another aspect, we provide the plating-free solid wire for arc welding wherein: MoS2 having a particle diameter of 0.1 to 10 xcexcm is preferably present in the pits and/or on the wire surface in an amount of 0.01 to 0.5 g per 10 kg of the wire.
In another aspect, we provide the plating-free solid wire for arc welding wherein: as the wire components, the wire preferably contains: C: 0.01 to 0.15 mass %, Si: 0.2 to 1.2 mass %, Mn: 0.5 to 2.5 mass %, P: 0.001 to 0.030 mass %, S: 0.001 to 0.030 mass %, and O: 0.001 to 0.020 mass %.
In another aspect, we provide the plating-free solid wire for arc welding wherein: the wire may contain Cu in an amount of not more than 0.05 mass %.
In another aspect, we provide the plating-free solid wire for arc welding wherein: the wire may contain Ti+Zr in an amount of 0.03 to 0.3 mass %.
In another aspect, we provide the plating-free solid wire for arc welding wherein: the wire may contain Mo in an amount of 0.01 to 0.6 mass %.
In the present invention, with such a configuration, even at the time point when the wire during welding has been fed to immediately above the chip, the lubricating properties are sufficiently kept. Accordingly, it becomes possible to implement a further stabilization of the arc and a further reduction in amount of generated spatters while holding the perfect feedability.
Further, the state where the K compound and MoS2 are present in the xe2x80x9cbottleneck-like and/or cave-like pitsxe2x80x9d, i.e., on the surface and/or immediately under the surface of the wire, and the state where an oil containing polyisobutene is present on the wire surface denote the following state. Namely, as schematically shown in FIG. 2, these functional materials are deposited as a thin film so as to coat the wire surface, or these functional materials are present in a large number of pits formed in the wire surface. These functional materials denote all of the K compound, MoS2, and the oil containing polyisobutene which will be taken out when the wire surface portion to a depth of 30 xcexcm from the wire surface is removed after acid pickling of the wire surface with a hydrochloric acid (HCl).
Other and further objects, features and advantages of the invention will appear more fully from the following description.